Compressor capacity control



Dec. 26, 1967 D. N. SHAW COMPRESSOR CAPACITY CONTROL Filed Sept. 27, 1965 xxx w t 2 2 BMW \2 w n 8 R N o n 3 u mm NQE ATTORNEY.

United States Patent 3,360,186 COMPRESSOR CAPACITY CONTROL David N. Shaw, Liverpool, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Sept. 27, 1965, Set. No. 490,612 6 Claims. (Cl. 230-24) ABSTRACT OF THE DISCLOSURE A control for regulating the capacity of reciprocating compressors through neutralizing the compressive effect of one or more of the compressor cylinders, the control incorporating a ballast chamber to reduce chatter of the principal pressure actuated unloader valve. The seating surfaces of the principal unloader valve are tapered to reduce any tendency of the aforesaid principal valve to chatter. The control functions to load and unload the compressor cylinder in response to pressure conditions within the crankcase compartment of the compressor.

This invention relates to control arrangements and, more particularly, to control arrangements for regulating the capacity of fluid compressors.

In copending application Serial No. 354,714, filed on March 25, 1964, there is disclosed a compressor capacity control apparatus which employs a movable piston type valve arranged to close an unloading port between certain compressor cylinders to render those compressor cylinders operative. The driving forces used to vary the position of the unloader valve of that capacity control arrangement are pressures generated by the compressor itself.

Where the aforementioned capacity control apparatus is used with reciprocating compressors, particularly large size reciprocating compressors, the unloading of one or more of the compressor cylinders often creates internal pressure pulsations which are both nonuniform and of relatively large amplitude. These pressure pulsations may cause fluttering or chattering of the unloader valve, a phenomenon which seems most prevalent just before seating of, or immediately following unseating of, the unloader valve.

It is a principal object of the present invention to provide a new and improved capacity control apparatus for compressors.

It is a further object of the present invention to provide an arrangement for dampening pressure pulsations within the power chamber of the unloader piston of a compressor capacity control apparatus.

It is an object of the present invention to provide a compressor capacity control of the type having-a compressor gas driven unloader valve incorporating means to reduce valve chatter inducing pressures thereon. Other objects of the invention will be readily perceived from the ensuing description.

This invention relates to a multi-cylinder compressor comprising in combination an unloading port between suction and discharge sides of at least one cylinder; a pressure actuated valve for closing the unloading port; passage means communicating the valve with relatively high pressure gas discharged from the compressor to move the valve to close the unloading port and load the cylinder; bias means opposing closing movement of the valve; bleed means for reducing gas pressure in the passage means to permit the bias means to move the valve to open the port and unload the cylinder; and means forming a chamber, the chamber forming means including an orifice connecting the chamber with the passage means, the orifice accommodating flow of gas between the chamber and the passage means to dampen chatter inducing pressure pulsations on the valve.

ICC

The attached drawing illustrates a preferred embodiment of the invention in which:

FIGURE 1 is a cross-sectional view of a four cylinder reciprocating type compressor embodying the control arrangement of the present invention;

FIGURE 2 is a sectional view of a portion of a compressor embodying the capacity control arrangement of the present invention; and

FIGURE 3 is a partial view on enlarged scale of the unloader valve shown in FIGURE 1.

Referring to FIGURE 1 of the drawing, a fluid compressor 10 embodying the control arrangement of the present invention is shown. While the control arrangement of the present invention is shown and decsribed as applied to a compressor of the reciprocating type, it is understood that the control arrangement is applicable to other types of compressors.

The compressor 10 is a four-cylinder compressor having a shell 2 forming cylinder banks 3 and 4. Each of the cylinder banks 3 and 4 include a pair of cylinders 11 opening into crankcase compartment 8. Pistons 14 in cylinders 11 are connected to the crankshaft 5 by connecting rods 6.

A suction manifold 22 is provided for introducing low pressure gas into the several cylinders. A discharge manifold 23 is provided for receiving the pressurized gas discharged from the cylinders. Discharge manifold 23 is provided with an outlet 7.

In the compressor 10, cylinder bank 3 is provided with capacity control for regulating the capacity of compressor 10. While compressor 10 is shown as a four-cylinder compressor having two banks of paired cylinders 3 and 4, it is understood that additional cylinder banks may be provided, some or all of which may be provided with capacity controls.

Referring to FIGURE 2, the cylinder 11 includes a cylinder head 12 secured to the compressor 10 by bolts 13. The piston 14 moves within the cylinder 11. A valve plate 15 is placed between the cylinder head 12 and the cylinder 11. Cylinder head gasket 16 and valve plate gasket 17 are disposed on opposite sides of valve plate 15. The cylinder communicates with the cylinder head through the discharge port 18 and suction port 19 in the valve plate 15.

Aflixed to the valve plate are a discharge valve 20 and a suction valve 21. On the suction stroke of the piston, gases are drawn into the cylinder through the suction port 19 from the suction manifold 22 through chamber 32. On the discharge stroke the compressed gas is forced into the discharge chamber 29 through the discharge port 18. When the cylinder is in loaded condition, the cylinder discharge pressure will force open the check valve 24 to permit passage of refrigerant gas into the discharge manifold 23. Check valve 24 is urged toward closed position by spring 26 disposed between valve 24 and support 25.

Within the cylinder head is a partition 27 which divides the head into a discharge chamber 29 and a suction chamber 30. The chambers 29 and 30 can be considered to be merely extensions of the discharge manifold and the suction manifold, respectively. The partition 27 includes an unloader port 33 to place the chambers 29 and 30 in communication with one another. Chamber 32 is placed in communication with suction manifold 22 by internal passages (not shown) in the compressor.

Referring to FIGURES 2 and 3 of the drawing, a piston-like valve 34 having valve face engageable with valve seat 101 in partition 27 to sealingly close unloader port 33 is provided. The head of the valve 34 is formedapparent hereinafter.

Spring 35, positioned in piston chamber 39 cm Spring ide 36 urges piston 34 in an opening direction. One end of spring 35 abuts retaining ring 37 secured to p1ston 34 and the other end engages retaining lip 38 of guide 36.

Spring guide 36 is hollow, the chamber 91 therewithm communicating with piston chamber 39 by means of a small passage 92. Chamber 91 serves to dampen or neutralize pressure pulsations in piston chamber 39, gas bleeding through passage 92 from chamber 91 into piston chamber 39 when pressures in chamber 91 exceed pressures in chamber 39, and vice versa. By dampening pressure pulsations in piston chamber 39, the tendency of valve 34 to chatter when seating and unseating is reduced or eliminated.

The capacity control 40 is secured to cylinder head 12. Gasket 42 is provided to prevent the leakage of the gases from the compressor.

Valve stem 56 is loosely positioned in opening 43 with opposite ends extending into chambers 46, 47. Control valve 55 is slidably disposed for limited relative movement on the reduced end of stem 56 in chamber 46. Control spring 62 urges valve 55 into abutment with stop collar 61 while spring 64 in chamber 47 urges valve stem 56 in a valve closing direction. Spring 64 is capable of overriding valve control spring 62.

A bleed passage 51 communicates chamber 46 with discharge passage 52. Passage 48 communicates chamber 46 with piston chamber 39. Cylinder head passage 53 communicates discharge passage 52 with compressor dis charge manifold 23. Passage 50 in cylinder head 12 interconnects passage 49 in control body 45 with passage 95 in the compressor shell 2. Passage 95 opens into the compressor crankcase compartment 8. Crankcase compartment '8 is less subject to internal compressor pressure fluctuations, such as caused when operating the compressor with one or more cylinders unloaded, than are the compressor suction and discharge manifolds. Using the more stable compressor crankcase compartment as the source of control pressure for capacity control 40 reduces pressure pulsation within control 40, and particularly within piston chamber 39.

A pressure differential control means 75 for regulating pressures in chambers 39, 46 is provided. Pressure differential control means 75 includes passage 71 between passage 50 and chamber 46 having closure means, ball valve 72, therefor. Spring 73 urges valve 72 in a closing direction. Cooperating screw and nut type adjusting means 74 regulate tension of spring 73.

A diaphragm 66 of capacity control 40 is arranged to abut valve stem 56. A spring 67, acting through diaphragm 66, urges valve stem 56 and valve 55 positioned thereon in a valve open direction, that is, cylinder unloaded position. Spring 67 is capable of overriding valve stem spring 64. Threaded cap 68 is provided for the purpose of adjusting the bias of spring 67. Diaphragm chamber 69 in control body 45 communicates with passage 50 by means of the clearance between valve stem 56 and the wall of opening 43, chamber 47 and passage 49.

During operation of the compressor 10, gas is drawn, on the suction stroke of the piston into the cylinder 11 from the suction manifold 22, through chamber 32, suction port 19 and suction valve 21. On the discharge stroke of the piston the cylinder suction valve 21 is closed and the gas is forced through discharge port 18 and discharge valve 20 into the discharge chamber 29. From the chamber 29, the gas flows by the check valve 24 into the discharge manifold 23 for discharge through discharge outlet 7.

Inasmuch as at least one of the other compressor cylinders is loaded at all times, a suitable pressure head is maintained in the discharge manifold 23. When the cylinder is loaded, that is, port 33 is closed by control piston 34, the discharge pressure of the loaded cylinder forces check valve 24 open to discharge pressurized gas into the 4 manifold 23. At all other times, check valve 24 is closed. The purpose of check valve 24 is to prevent pressurired gas in discharge manifold 23 from flowing into the suct1on manifold 30 while permitting the pressurized gas obtained from the cylinder during the loaded condition thereof to discharge into the discharge manifold 23.

When control valve 55 communicates bleed passage 51 with passage 49, reduced pressure in piston chamber 39 is insuflicient to overcome spring 35. Accordingly, piston 34 is retracted. The compressor cylinder is therefore unloaded due to the communication of discharge chamber 29 with suction chamber 30 by means of port 33. Valve 72 of pressure differential control means 75, under the influence of spring 73, closes passage 71.

The reduced pressure in the piston chamber 39 is effected by bleeding the gas from the compressor discharge manifold 23 into the compressor crankcase compartment 8 through bleed passage 51, valve 55 and passages 49, 50, 95. The pressure of the compressor discharge gas is re duced because the rate of bleed into crankcase compartment 8 is more than the rate of supply through the bleed pass-age 51. This reduced pressure is insufficient to overcome the spring 35 which maintains piston 34 retracted. Discharge pressure in the discharge manifold 23 (from the working cylinders) will close check valve 24 isolating the compressor discharge manifold from the individual unloaded cylinder manifolds.

An increase in load on the compressor is reflected by an increase in pressure in both suction manifold 30 and crankcase compartment 8. Diaphragm chamber 69, com municating with crankcase compartment 8 via passages 49, 50, and opening 43 in control body 45, reflects a similar pressure increase. The increased pressure in chamber 69 moves diaphragm 66 against spring 67 and valve stem 56, under the influence of spring 64, moves control valve 55 toward closed position. It is under-stood that spring 64 is capable of overriding valve spring 62 holding control valve 55 against stop collar 61. The increase in crankcase compartment pressure required to permit diaphragm 66 to overcome spring 67 may be varied by ad.- justment of cap 68.

As control valve 55 moves toward valve seat 57 and closed position, the rate of bleed of discharge gas from bleed passage 51 into crankcase compartment 8 through valve 55 decreases with a resultant increase in pressure. Valve 72 of pressure differential control means 75 is closed so that valve 55 alone regulates the rate at which dischargegas is bled into crankcase compartment 8.

As control valve 55 nears closed position, the build=up of pressure in chamber 46 overcomes valve control spring 62 and valve 55 snaps shut to interrupt the bleed of discharge gas into crankcase compartment 8. The increased pressure in piston chamber 39 moves piston 34 against the urging of spring 35 to close port 33 thereby loading the cylinder.

At a predetermined valve chamber pressure, the force of spring 73 holding valve 72 of pressure differential control means 75 closed is overcome to uncover passage 71 and bleed gas from control valve chamber 46 into the crankcase compartment 8. By this arrangement a predetermined piston closing pressure may be maintained in piston chamber 39. It is understood that the force of spring 73 and thus the control pressure in valve chamber 46 may be regulated by adjustment of screw means 74.

A decrease in compressor load is evidenced by a decrease in pressure in both suction manifold 30 and crankcase compartment 8. Diaphragm chamber 69 reflects a similar decrease and moves valve stem 56 in an opening direction against the force of spring 64. Control valve 55, capable of limited movement relative to valve stem 56 remains closed.

As crankcase compartment pressures decrease, diaphragm 66 opens control valve 55 to bleed relatively high pressure gas in chambers 39, 46 into the crankcase compartment 8. The resulting decrease in pressure in piston chamber 39 permits spring 35 to unseat valve 34. When valve 34 is first unseated 'or cracked, the rush of high pressure gas from discharge chamber 29 around valve 34 and through port 33 into suction chamber 30 creates a relatively 'low pressure condition at the face 102' of valve 34 which tends to reclose valve 34 in opposition to the bias of spring 35. Where the instantaneous pressure forces acting on valve 34 are sufiicient to overcome spring 35, valve 34 recloses. As valve 34 recloses, the low pressure condition created by the rush of discharge gas around valve 34 into the suction compartment is removed and spring 35 reopens valve 34 which, on the re-establishment of the aforementioned low valve face pressure, may again close, and then reopen, etc. Continued opening and closing, or chatter, of valve 34 not only delays unloading of the compressor cylinder but may damage the unloader components. The frusto-conical shape of head 102 of valve 34 reduces the aforementioned pressure effect on face 102' of valve 34 by providing a relatively smooth and contiguous flow path during opening movement of valve 34.

Control spring 62 moves control valve 55 against stop 61. Reduced pressure is maintained in piston chamber 39 by the flow of discharge gas through bleed passage 51 and control valve chamber 46 into crankcase compartment 8 in the manner described heretofore.

Valve stem 56, positioned in opening 43 in control body 45 communicating diaphragm chamber 69 with suction pass-age 49, restricts the elfective size of opening 43. During movement of control valve 55 in an opening direction, the bleed of relatively high pressure gas in control valve chamber 46 around valve 55 into passage 49 may result in a surge of pres-sure in passage 49. The reduced size of opening 43 effectively prevents this pressure surge from affecting diaphragm 66.

While the present invention is shown and described in conjunction with a compressor capacity control 'of the type disclosed in the aforesaid copending application Serial No. 354,714, wherein a pressure actuated diaphragm 66, acting through control valve 55, regulates movement of the piston-like unloader valve 34, it is understood that the present invention is not limited thereto but may be incorporated in compressor capacity controls having other controlling arrangements, such as the solenoid regulated capacity control of US. Patent No. 3,119,550.

While I have described a preferred embodiment of the invention, it will be understood that the invention is not limited thereto since it may be otherwise embodied in the scope of the following claims.

'I claim:

1. In a multi-cylinder compressor including a cylinder head having an unloading port between suction and discharge sides of at least one cylinder, the combination of a hollow piston-like valve having a head portion and a depending skirt portion, said valve being movably supported by said cylinder head for relative movement to open or close said port, the interior of said valve including said depending skirt portion cooperating with said cylinder head to form a first chamber, the dimension of said first chamber varying in accordance with movement of said piston-like valve; passage means communicating said first chamber with relatively high pressure gas discharged from said compressor to move said valve to close said port and load said cylinder; bias means urging said valve in a port opening direction; bleed means for reducing gas pressure in said passage means to reduce pressure in said first chamber and permit said bias means to move said valve to open said port and unload said cylinder; means forming a second closed chamber of fixed dimension within said first chamber; and an orifice communicating said first chamber with said second chamber to permit fiow of pressure gas between said first and second chambers to dampen chatter inducing pressure pulsations on said piston-like valve.

2. The compressor according to claim 1 in which said valve is arranged for reciprocal movement toward and away from said port, said valve head portion being adapted on closure of said valve member to overlay said unloading port.

3. The compressor according to claim 2 in which said valve head is domed so as to project outwardly in the direction of said unloading port.

4. The compressor according to claim 1 in which said compressor includes a crankcase compartment, said bleed means being adapted to communicate with said compressor crankcase compartment whereby relatively high pressure discharge gas in said passage means is bled into said compressor crankcase compartment to reduce pressures in said pas-sage means and permit said bias means to open said control piston.

'5. In a reciprocating compressor, the combination of a cylinder including a movable piston therein, a suction manifold, a discharge manifold, a crankcase compartment, a cylinder head for the compressor, said cylinder head including a partition separating a discharge chamber from a suction chamber, said partition having an opening therein, normal-1y open pressure actuated means for closing said partition opening, a bleed passage communioating said discharge manifold with said pressure actuated means and said crankcase compartment, means forming a closed chamber having a relatively small opening communicating said chamber with said bleed passage, said opening permitting flow of pressure gas between said bleed passage and said chamber to dampen pressure pulsations on said pressure actuated means, means for controlling the pressure in said bleed passage including means to regulate flow through said bleed passage, and means responsive to changes in crankcase compartment pressure to actuate said flow regulating means to control pressure in said bleed passage including a control pressure powered operator engagable with said flow regulating means whereby upon a predetermined increase in crankcase compartment pressure said operator actuates said flow regulating means to decrease flow through said bleed passage so that said pressure actuated means closes said partition opening to load said com-pressor, and upon a predetermined decrease in crankcase compartment pressure said operator actuates said flow regulating means to increase flow through said bleed passage so that said pressure actuated means open-s said partition opening to unload said compressor.

6. The compressor according to claim 5 in which said pressure actuated means comprises a piston-like member having a head portion and a depending skirt portion, said piston-like member head portion having a frusto-conical projection adapted when said valve member is adjacent said partition opening to provide a controlled flow path for the discharge gas stream flowing around said valve member into said partition opening and said suction chamber whereby the pressureeffect from said gas stream on said valve vmember is reduced.

References Cited UNITED STATES PATENTS 1,897,292 2/1933 Babitch 103-224 2,043,453 6/1936 Vicker-s 137-469 2,151,501 4/1939 Corcoran 137-469 2,350,518 -6/ 1944 Morrison 230-24 2,462,039 2/ 1949 Gibson 230-31 2,761,616 9/1956 Newton 230-31 2,836,345 5/1958 Gerteis 230-31 2,973,133 2/ 1961 Newton 230-26 3,021,790 2/ 1962 Brunson 103-42 3,119,550 1/1964 West et al 230-2-2 3,184,151 5/ 1965 Shaw 230-22 DONLEY J. STOCKING, Primary Examiner.

W. J. KRAUSS, Assistant Examiner. 

1. IN A MULTI-CYLINDER COMPRESSOR INCLUDING A CYLINDER HEAD HAVING AN UNLOADING PORT BETWEEN SUCTION AND DISCHARGE SIDES OF AT LEAST ONE CYLINDER, THE COMBINATION OF A HOLLOW PISTON-LIKE VALVE HAVING A HEAD PORTION AND A DEPENDING SKIRT PORTION, SAID VALVE BEING MOVABLY SUPPORTED BY SAID CYLINDER HEAD FOR RELATIVE MOVEMENT TO OPEN OR CLOSE SAID PORT, THE INTERIOR OF SAID VALVE INCLUDING SAID DEPENDING SKIRT PORTION COOPERATING WITH SAID CYLINDER HEAD TO FORM A FIRST CHAMBER, THE DIMENSION OF SAID FIRST CHAMBER VARYING IN ACCORDANCE WITH MOVEMENT OF SAID PISTON-LIKE VALVE; PASSAGE MEANS COMMUNICATING SAID FIRST CH AMBER WITH RELATIVELY HIGH PRESSURE GAS DISCHARGED FROM SAID COMPRESSOR TO MOVE SAID VALVE TO CLOSE SAID PORT AND LOAD SAID CYLINDER; BIAS MEANS 